The present invention relates to lighting control systems and, more particularly, relates to a control system for providing variable arc current to one or more fluorescent lamps, including an improved start-up circuit for providing a bias voltage supply to various system components.
Fluorescent lamps are gas discharge lamps that are based on Hg vapor which, when excited, provides a low intensity spectral line of visible light and several high intensity lines of ultra-violet light, that are converted to visible light by the phosphor coating on the interior surface of the lamps. Fluorescent lamps were perfected as an alternative to incandescent lamps, and have since replaced the incandescent lamps in most commercial and industrial applications. The fluorescent lamp has a substantially longer life than the incandescent lamp which results in reduced maintenance costs. The fluorescent lamp also provides a more distributive light source which is two to six times more efficient than incandescent lighting in terms of luminous flux per unit of electric power consumed.
Since the fluorescent lamp has no inherent current limiting mechanism when operated by a voltage source, the fluorescent lamp requires an auxiliary device to first ignite the lamp arc and then, after ignition has occurred, to control the amplitude of the arc current. Without an auxiliary device to stabilize or limit the arc current, the lamp arc would exceed its current rating and thus, the fluorescent lamp would be damaged. In conventional systems the auxiliary device has been combined into a single device called a ballast. The ballast provides a means for igniting the lamp arc and also provides a fixed value of arc current to the lamps. A shortcoming of the fixed value of arc current lighting is that it wastes energy. Underlighted conditions are often due to light absorbing dust on the lamp and the deterioration of the phosphor coating on the inside wall of the fluorescent tube. To reduce the effect of the underlighted conditions, designers overlight the area when the lamps are new and lumina are clean so there is still sufficient light remaining when lamp light output reaches depreciated states. Therefore, much of the electric energy that can be saved by using fluorescent lighting is lost due to the industrial practices of maintaining the use of fixed value arc current lamp operation.
One prior art technique used to reduce wasteful overlighting and promote energy savings is disclosed in U.S. Pat. No. 5,483,127 to Widmayer et al. The Widmayer et al. patent discloses a fluorescent lighting control system which automatically adjusts the arc current to a fluorescent gas discharge lamp. The variable arc current lighting system includes a sensor that senses ambient light and the output light of the lamp and provides a corresponding electrical signal to an electronic circuit. The electronic circuit controls the frequency of repetition of alternating on-off periods of electronic switches. As the frequency of switching the electronic switches is increased or decreased, the effective impedance value of the current limiting inductances that are connected in series with each lamp is controlled. Thus, the current amplitude is increased or decreased by controlling the switching frequency of the electronic switches. By reducing the arc current supplied to a fluorescent lamp, the lamp operates at less than rated wattage thereby reducing electrical consumption. The variable-arc lighting system also includes a start-up circuit which provides a voltage supply to the internal electronic circuits. However, this lighting control system is complex, expensive to produce and difficult to troubleshoot and repair.
Another prior art variable-arc lighting system is the Mark VII system made by Precision Lighting, Inc., of Rockville, Md. The Mark VII system operates on the same principle as the Widmayer et al. patent, but has been simplified to reduce cost and size. The Mark VII system includes electronic circuits that control the switching frequency of electronic switches in order to control the arc current in a fluorescent lamp. The Mark VII system also includes a start-up circuit which provides a voltage supply to various internal electronic circuits.
One disadvantage of the start-up circuits in the Widmayer et al. patent and in the Mark VII system is that the start-up circuits are generally unreliable. The start-up circuit includes a power transistor that is driven on and off to provide a voltage supply to the internal electronic circuits. When the start-up circuit has completed its operation, and the ballast is in normal operation, there is a continuous high voltage present on the power transistor. The high voltage exceeds the rating of the power transistor and over a period of time the power transistor can be damaged. Replacing the power transistor with a different type of transistor having higher voltage ratings would require a different control circuit, thus increasing the need for circuit components and, as a result, increasing costs.
Another disadvantage of the start-up circuits in the Widmayer et al. patent and in the Mark VII system is that the power transistor is not always capable of being turned off when the main input voltage source is abnormally low. If the power transistor remains on or in a conducting state for a considerable time period, the electronic elements and circuits which are electrically connected to the power transistors will receive continuous current. These electronic elements and circuits, and the transistor itself, can be damaged as a result of overheating due to the continuous current flow.
A further disadvantage of the start-up circuits in the Widmayer et al patent and in the Mark VII system is that the start-up circuit includes a single rectifier bridge in order to provide a bias voltage to multiple electronic circuits and as a consequence, the multiple electronic circuits are not electrically isolated from each other, so that the unequal voltage requirements of the different circuits is not easily provided for.
In accordance with the present invention, there is provided a control system for providing variable arc current control of a lighting system, said control system comprising: an input power factor correction means including means for converting AC power from an AC power source into converted DC power, said input power factor correction means boosting said converted DC power so as to provide boosted converted DC power; a lamp unit comprising at least one fluorescent gas discharge lamp; switching means for controlling application of said boosted converted DC power to said lamp unit; an output power conditioning means, connected to said input power factor correction means and to said switching means, for controlling operation of said switching means so as to control application of said converted DC power to said lamp unit; and
a start-up circuit including a starting means for providing a starting voltage to said output power conditioning means, said start-up circuit further comprising a plurality of voltage doubling rectifier circuits for providing a bias voltage supply to said output power conditioning means and to said input power factor correction means.
Advantageously, one of the plurality of voltage doubling rectifier circuits of the start-up circuit is electrically connected to the input power factor correction means and a further one of the plurality of voltage doubling rectifier circuits of the start-up circuit is electrically connected to the output power conditioning means.
Preferably, one of the plurality of voltage doubling rectifier circuits comprises a first pair of diodes and a further one of said plurality of voltage doubling rectifier circuits comprises a second pair of diodes.
Preferably, the starting means includes a resistor electrically connected in series with a capacitor for providing a starting voltage to the output power conditioning means.
Advantageously, the start-up circuit includes a first zener diode electrically connected to the input power factor correction means so as to limit and regulate said bias voltage supply and the start-up circuit also includes a second zener diode electrically connected to the output power conditioning means so as to limit and regulate said bias voltage supply.
Advantageously, at least one fluorescent gas discharge lamp includes electrodes and the output power conditioning means supplies a heating voltage for said electrodes of said at least one arc discharge lamp.
Preferably, the output power conditioning means supplies arc current for said lamp unit and the input power factor correction means and the output power conditioning means comprise integrated circuits.
Advantageously, the switching means provides alternate application of positive and negative DC voltages to the lamp unit.
Preferably, the input power factor correction means includes an analog multiplier connected to a switching transistor for driving said switching transistor with a variable frequency pulse in order to control boosting of said converted DC power.
Advantageously, the output power conditioning means further comprises a feedback means for sensing light of said lamp unit and automatically adjusting the current level supplied to said lamp unit in accordance with the sensed light of said lamp unit.
Preferably, said feedback means includes at least one photoresistor electrically connected to at least one capacitor in order to form an RC time constant circuit.
In accordance with another aspect of the invention, there is provided a control system for providing variable arc current control of a lighting system, said control system comprising: an input power factor correction means including a means for converting AC power from an AC power source into converted DC power, said input power factor correction means boosting said converted DC power so as to provide boosted converted DC power; at least one lamp unit comprising at least one fluorescent gas discharge lamp including electrodes; a main output transformer having a primary winding and at least one secondary winding, said primary winding being connected to said input power factor correction means and said at least one secondary winding being connected to said electrodes and to said at least one lamp unit; a switching means connected to said primary winding of said main output transformer; output power conditioning means, connected to said input power factor correction means, and to said switching means, for controlling said switching means to provide voltage to said primary winding of said main output transformer so as to produce a resultant voltage on said at least one secondary winding of said main output transformer and thus provide a heating voltage to said electrodes and variable arc current to said at least one lamp unit; and
a start-up circuit including a starting means for providing a starting voltage to said output power conditioning means, said start-up circuit further comprising a plurality of voltage doubling rectifier circuits for providing a bias voltage supply to said output power conditioning means and to said input power factor correction means.
Preferably, the starting means includes a resistor electrically connected in series with a capacitor for providing a starting voltage to the output power conditioning means.
Advantageously, the start-up circuit includes a first zener diode electrically connected to the input power factor correction means so as to limit and regulate said bias voltage supply and the start-up circuit includes a second zener diode electrically connected to said output power conditioning means so as to limit and regulate said bias voltage supply.
In accordance with a further aspect of the invention, there is provided a control system for providing variable arc control of a lighting system including at least one lamp unit, said control system comprising: converting means for converting AC power from an AC power source into converted DC power, said converting means including an input power factor correction means for boosting said converted DC power to produce boosted DC power; switching means for controlling application of said converted DC power to the at least one lamp unit;
output power conditioning means connected to said switching means for controlling operation of said switching means; and
a start-up circuit connected to said input power factor correction means and to said output power conditioning means, said start-up circuit including:
a starting means for providing a starting voltage to said output power conditioning means so as to control said switching means to provide an operating voltage to said input power factor correction means to produce a boosted operating voltage;
a first voltage doubling rectifier circuit and a first zener diode electrically connected to said input power factor correction means for receiving said boosted operating voltage and for providing a regulated bias voltage supply to said input power factor correction means; and
a second voltage doubling rectifier circuit and a second zener diode electrically connected to said output power conditioning means for receiving said boosted operating voltage and for providing a regulated bias voltage supply to said output power conditioning means.
Further features and advantages of the present invention will be set forth in, or apparent from, the detailed description of preferred embodiments thereof which follows.